Extractive distillation of isopropyl alcohol with an ether solvent recovered from the initial feed

Abstract

A water-free mixture of isopropyl alcohol, diisopropyl alcohol, diisopropyl ether and by-products is made by the catalytic hydration of propylene in the gaseous phase at temperatures of 140°-170°C under pressures of 25-40 atmospheres gauge. A water-to-propylene molar ratio of 0.1 to 0.25:1 is maintained in the hydration reaction. The crude product from the hydration reaction is dehydrated or dewatered in two columns without using a foreign withdrawing agent. Instead, diiosopropyl ether formed in the process itself is utilized as the withdrawing agent which is subsequently added to the water-free mixture together with additionally formed by-products. The water-free mixture formed according to the process can be used directly as an additive to gasoline fuel for motor vehicles.

We claim: 
     
       1. Process for recovering a water-free mixture of isopropyl alcohol, diisopropyl ether and, as by-products, n-propanol, acetone, hexanol and hydrocarbons, from the catalytic hydration of propylene in the gaseous phase at temperatures of 140°-170°C and pressures of 25-40 atmospheres gauge which consists essentially of: a. conducting the hydration reaction with a water-to-propylene molar ratio of 0.1 to 0.25 to produce a crude reaction product mixture containing water, isopropyl alcohol, diisopropyl ether and said by-products;   b. concentrating the crude reaction product from (a) by distillation in a first column, withdrawing water as the sump product until the mixture is close to the azeotropic concentration of the isopropyl alcohol-water azeotrope; and   c. extractively distilling at least a portion of the concentrated mixture from (b) in a second column withdrawing said water-free mixture as the sump product and a mixture consisting of diisopropyl ether and said by-products formed in hydration step (a) prior to steps (b) and (c) and recycling said mixture of diisopropyl ether and by-products to the top of said second column, said diisopropyl ether formed exclusively as a byproduct of the hydration reaction serving as the extracting agent for the distillation in the second column, while eliminating the need for an external source of diisopropyl ether make-up.   
     
     
       2. Process of claim 1 wherein the first column is operated at a pressure of 3 to 7 atmospheres, the latent heat of head product from said first column serving to heat a reboiler for the second of said columns. 
     
     
       3. Process of claim 1 wherein a mixture of water, isopropyl alcohol, diisopropyl ether and higher alcohols is recovered from the second column and recycled to the first column.